一种更轻松的发现文本写作方向的方法 [英] A lighter way of discovering text writing direction

问题描述

我想确定字符串的书写方向，以便我可以在 CALayer 中正确呈现从右到左的语言，例如阿拉伯语.

I want to determine the writing direction of a string so that I can render Right-to-Left languages such as Arabic correctly in a CALayer.

所以我有这个方法

+(UITextAlignment)alignmentForString:(NSString *)astring
{
    UITextView *text = [[UITextView alloc] initWithFrame:CGRectZero];
    text.text = astring;

    if ([text baseWritingDirectionForPosition:[text beginningOfDocument] inDirection:UITextStorageDirectionForward] == UITextWritingDirectionRightToLeft) {
        return UITextAlignmentRight;
    }

    return UITextAlignmentLeft;

}

工作正常但感觉有点沉重，只是为了发现对齐我的文本的方式，特别是因为它在 drawInContext 中被调用(尽管相对不频繁).

Works fine but feels a little heavy just for the purpose of discovering which way to align my text especially as its been called in drawInContext (although relatively infrequently).

是否有更轻松的方法来确定给定字符串的书写方向，或者我应该在过早优化的基础上坚持下去.而且它必须对 iOS 5 友好.

Is there a lighter way of determining the writing direction for a given string or should I just stick with this under the basis of premature optimisation. And its got to be iOS 5 friendly.

推荐答案

问题中的代码虽然功能性非常昂贵.通过分析器运行它，您会发现当在图层的 drawInContext 方法中使用时，它在 UITextView.setText 中花费了接近 80% 的时间.

The code in the question although functional is brutally expensive. Run it through a profiler and you will find that it spends close to 80% of the time in UITextView.setText when used in the drawInContext method for a layer.

大部分答案都在检测 NSString 的语言

因此更好的形式是...

a better form is thus...

+(UITextAlignment)alignmentForString:(NSString *)astring
{

    if (astring.length) {

        NSArray *rightLeftLanguages = @[@"ar",@"he"];

        NSString *lang = CFBridgingRelease(CFStringTokenizerCopyBestStringLanguage((CFStringRef)astring,CFRangeMake(0,[astring length])));

        if ([rightLeftLanguages containsObject:lang]) {

            return UITextAlignmentRight;

        }
    }

    return UITextAlignmentLeft;

}

因为阿拉伯语和希伯来语是 CFStringTokenizerCopyBestStringLanguage 可以检测到的唯一从右到左的语言，并且还应该涵盖波斯语、乌尔都语和意第绪语，尽管我还没有测试过.

As Arabic and Hebrew are the only Right-to-Left languages detectable by CFStringTokenizerCopyBestStringLanguage and should also cover Persian, Urdu and Yiddish though I havent tested that.

另见http://en.wikipedia.org/wiki/Right-to-左

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